The present invention relates to a remaining paper detection apparatus for detecting a paper sheet left on a convey board arranged between the feeder and printing unit of a sheet-fed rotary printing press.
Generally, in the printing operation, the required quality is confirmed by test printing of a proofing print, printing copy, or the like, and thereafter final printing is performed. Test printing is repeated until quality matching is confirmed. Even in final printing, various operations, e.g., a blanket cleaning work, are performed as required in order to maintain the printing quality. In this manner, final printing is performed repeating interruption and resumption of printing, and accordingly paper feeding is performed repeating interruption and resumption. Therefore, a state wherein a fed paper sheet remains on a convey board often occurs.
Since a remaining paper sheet is not fed with a normal timing, misregistration may occur or the paper sheet may skew. If the paper feed operation is resumed while leaving the remaining paper sheet as it is, the paper sheet may be torn at the register or a torn paper piece may enter into the printing unit. To remove this torn paper piece, the blanket, the ink roller, the dampening roller, and the like must be cleaned unnecessarily.
If the paper sheet in a bent state is conveyed between printing units, it may damage the blanket or the respective portions of the machine, or be caught in the ink roller or the like. When such an accident occurs, an extra time is required to settle it, leading to a decrease in productivity and quality. Conventionally, the operator himself visually confirms the remaining paper sheets before the start of paper feed operation, imposing an extra load on the operator.